Population genetics of western bean cutworm in putative ancestral and derived ranges

The western bean cutworm (WBC), Striacosta albicosta, is a primary pest in corn (Zea mays) and dry beans (Phaseolus spp.) in Canada and the Corn Belt. It directly damages corn kernels, leading to secondary fungal infection (ear rot). Managing WBC faces widespread resistance to transgenic corn expressing Bacillus thuringiensis (Bt) Cry1F insecticidal protein, while Vip3A corn remains effective but concerns of resistance exist. In Mexico the insect is a minor under-studied corn pest, wherein geographic distribution and host range remain relatively unknown. Considering that Mexico is the cradle of corn and bean domestication by indigenous people, the strong association of WBC with these plants, and its long-range migratory capabilities, we tested population genetic hypotheses considering the country as the ancestral source of US and Canada populations. We collected WBC moths with pheromone traps over three years in Mexico, from areas with cultivated corn and bean. These WBC captures indicated a marked highland, Y-shaped geographic distribution, across the inland piedmont of the western and eastern Sierra Madre Mountain ranges. These populations apparently coalesce in the Trans-Mexican Volcanic Belt. Differentiation in mitochondrial DNA sequence between WBC in Mexico and the United States will predict the ancestral source population, and provide indirect estimates of migration and isolation-by-distance on a near-continental scale. These data provide initial insights into WBC across Mexico and their relationship to those in the US and Canada, and population genetic estimates will be useful for predicting the rate at which resistance alleles may spread across the WBC population.